Function
- Assign time history functions for time history analyses.
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For convenience, midas Civil supports the following 3 data entry methods:
1. Save and retrieve frequently used time history loads in and from files
2. Access the built-in time history loads from the database
3. The user directly enters the time function data
Call
From the main menu, select [Load] tab > [Type : Dynamic Loads] > [Time History Analysis Data] group > [Time History Functions]
Input
Add Time Function
Click 'Add Time Function' when the time forcing function is of random type or a walking load.
Add Sinusoidal
Click 'Add Time Sinusoidal' when the time forcing function is sinusoidal.
Modify/Show
Select a time forcing function from the list in the dialog box and click 'Modify/Show'.
Delete
Select a time forcing function from the list in the dialog box and click 'Delete'.
Add/Modify/Show Time History Functions dialog box
Function Name
Enter the name of the time history function, which will be used for applying time history loads in "Dynamic Nodal Loads", "Ground Acceleration"or "Time Varying Static Loads". In the case of a walking load or earthquake data, the name may be automatically selected.
Time Function Data Type
Select a type of Time History Data.
Normalized Accel. : Values obtained through Time History Accelerations divided by the gravitational acceleration
Acceleration : Time history accelerations
Force
Moment
Normal : Non-dimensional
Force or Moment is selected to enter the time history loads as dynamic nodal loads in the Dynamic Nodal Loads function. Normalized Accel. or Acceleration is selected to enter the time history loads as ground accelerations in the Ground Acceleration function. Normal is selected to enter the time history loads as time dependent static loads in the Time Varying Static Loads function.
Scale Factor
Specify a multiplier for Time History Data.
If the user modifies Time Function Data Type while a time history load has been entered, only the units of the data will be changed, and the data (corresponding values) themselves will not be changed to the units of the revised Data Type. By using Scale Factor, all the values of the time history data can be simply revised.
For example, when the user enters 0.1g in Normalized Acceleration and subsequently changes the units to Acceleration, the magnitudes of the values will not be changed but remain as the entered value, 0.1m/s^2. In order to change 0.1g in the units of m/s^2, 9.8 needs to be entered in the Scale Factor, since 0.1g=0.98m/s^2.
Gravity
Display the applied acceleration of gravity, which may be revised in Model > "Structure Type".When the time forcing function is entered using the Normalized Acceleration type, it will be divided by the Gravitational Acceleration for analysis.
Graph Options
Specify whether or not to produce Graph in Log Scale.
Description
Enter a brief description of Time History Function.
Import File
Enter the time history loads by reading previously created files. The data are saved with '.sgs' or '.thd' extension and are written according to the following formats.
'fn.sgs' file type
| *SGSw | To define that the file is in "Seismic Data Generator" data format which is a MIDAS/Civil module that auto-extracts seismic data |
|---|---|
| *TITLE, Elcentro 1940, N-S Component | - |
| *X-AXIS, Second | - |
| *Y-AXIS, Normalized Acceleration | - |
| *UNIT&TYPE, GRAV, ACCEL | - |
| *FLAGS, 0, 0 | - |
| *DATA | - |
| 1.00000E-010, 3.50102E-001 | - |
| 5.00000E-002, 3.82861E-001 | - |
| 1.00000E-001, 5.08226E-001 | - |
| 1.50000E-001, 5.17459E-001 | - |
| : | - |
'fn.thd' file type
| Option | ** Comments - Entry allowed anywhere |
|---|---|
| - | *UNIT, M , N - Length: MM, CM, M, INCH, FEET, GRAV allowed |
| - | Load: KG, TON, KN, LBF, KIP |
| - | *TYPE, ACCEL - ACCEL, FORCE, MOMENT allowed |
| Requirement | *Data |
| - | X1 , Y1 (x : Time, X : Time Function) |
| - | X2 , Y2 |
| - | X3 , Y3 |
| - | : |
Example of fn.thd input
Earthquake
Create time history loads by reading earthquake records from the database. There are 32 types of built-in seismic accelerations in the database.
Add/Modify/Show Time History Functions dialog box
- Access the built-in time history functions from the midas Civil database
Earthquake
Create time history loads by reading earthquake records from the database.
There are 32 types of built-in seismic accelerations in the database.
- Enter directly the time history functions in the entry fields in the Add/Modify/Show Time History Functions dialog box
The user directly enters the time and the values of the time history function in the entry fields to the left of the dialog box.
Data entry method by clicking Add Sinusoidal.
Function Name
Enter the name of the time forcing function, which will be used for applying time history loads in "Dynamic Nodal Loads", "Ground Acceleration" or "Time Varying Static Loads".
Time Function Data Type
Assign the type of data to be entered.
Normalized Accel : Values obtained by dividing the time history acceleration by the acceleration of gravity
Acceleration : Time history acceleration
Force
Moment
Normal : Non-dimensional
When Force or Moment is assigned, the time forcing function is used to enter the Dynamic Nodal Loads function and when Normalized Accel. or Acceleration is assigned, it is used to enter the Ground Acceleration function. When Normal is assigned, a static load is defined to vary with time as a time history load in Time Varying Static Loads.
Parameters constituting the Sinusoidal Functions
A, C are constants, f is the frequency of excitation, D is the Damping Factor, PA is the Phase Angle.
When the time forcing function is entered in the form of a harmonic function, specify the parameters required in Sinusoidal Function. Click Redraw Graph to display the graph of the forcing function to the right and click OK to save the time forcing function.